• James, Peter
• Beswick, Jack
• Jivkov, Ap
• Sherry, Andrew H.

Abstract

Non heat-treated welds in reactor pressure vessel structures are subjected to residual stress fields from welding, and the ferritic steels within the structures are susceptible to embrittlement from neutron irradiation, increasing the probability of cleavage fracture. This paper presents results from an on-going project to better understand and quantify the effects of constraint on cleavage fracture in such steels under various initial stress and strain conditions. The conditions investigated simulate non heat-treated welds in reactor pressure vessel structures. Previous work (Mahmoudi et al., 2008) has demonstrated that a residual stress field introduced through a double side punching method ahead of a crack serves to reduce the constraint parameter Q for high constraint geometries, but increase Q for low constraint geometries (Beswick, et al., 2015) (Hurlston et al., 2011). Such results, in conjunction with experimental failure data, have been used to postulate a failure curve in J-Q space (where J is the usual crack driving force), which could be used as a two-parameter fracture toughness in defect tolerance assessments. What was not previously considered was whether this failure curve extended into a region for very shallow cracks (i.e. very low Q) under similar initial conditions.<br/>This paper includes findings from experiments that consider such very low constraint geometries. Specifically, fracture toughness tests were carried out on three-point bend specimens with normalised crack depths of a/W=0.4, 0.2 and 0.05. Initially, experiments were performed to reproduce the previous tests on higher constraint geometries without residual stress (Hurlston et al., 2011) for control and validation purposes. Following this, tests were conducted with and without the introduction of a similar residual stress field on the very low constraint geometries. The test results are presented in J-Q space and the paper includes comments on the applicability of a two-parameter fracture toughness curve that could be used under these initial conditions, and highlights the points requiring further experimental and theoretical investigation.<br/>

Topics

• impedance spectroscopy
• experiment
• crack
• steel
• fracture toughness